Various fluoran derivatives are already well-known and are used as dye precursors for pressure-sensitive papers or heat-sensitive papers, e.g., as disclosed in U.S. Pat. No. 3,825,432; West German Patent Application (OLS) No. 2,262,127; and Japanese Patent Publication (examined) No. 38245/76. None of the dye images obtained from these known fluoran derivatives are pure black and these known fluoran compounds suffer from the defect that they themselves are unstable in the atmosphere, produce dyes with inferior fastness to light, moisture, etc., and so on.